mobility and diet in prehistoric denmark: strontium

DANISH JOURNAL OF ARCHAEOLOGY 2020, VOL 9, 1-29, https://doi.org/10.7146/dja.v9i0.116301 1

1. Introduction

The geographical setting of the Limfjord area in the northern part of the Jutland peninsula (Fig-ure 1) by and near the sea as well as a natural communication port between east and west, has made this area one of Denmark’s important nodal points for long distance communication and trade (Kristiansen 1987; 1998; Birkedahl and Johansen 2000; Kristiansen and Larsson 2005; Nielsen 2011). This has been the case since the Ertebølle culture when people lived as hunter-gather-fish-ers, leaving behind the famous kitchen middens (Andersen 2008), to the Bronze Age when a concentration of mounds and grave goods show the importance of the area (Bech 2003), to the Viking Age sites of Sebbersund as ports of trade (Price et al., 2012) as well as the circular fortress-

es of Fyrkat and Aggersborg constructed during the reign of Harald Bluetooth (Roesdahl 2008). See Figure 2 for an overview of the archaeological time periods.

As a nodal communication port, Limfjord’s social and economic changes through time may be related to human mobility and consequently to contact with other cultures. Recently, ancient DNA analyses have revealed several large scale migrations in Europe during the Neolithic, as well as during the Late Neolithic/Early Bronze Age transition (Haak et al., 2015; Allentoft et al., 2015). In Scandinavia, recent investigations also address aspects of palaeomobility in Prehistoric Scandinavia from the Mesolithic to the Viking Age e.g. (Sjögren et al., 2009; Frei et al., 2015a; Frei et al., 2015b; Price et al., 2011; Harvig et al., 2014; Bergerbrant et al., 2017; Eriksson et al.,

Mobility and diet in Prehistoric Denmark: strontium isotope analysis and incremental stable isotope analysis of human remains from the Limfjord area

Laura G. van der Sluis1,5,6, J.Stephen Daly2,3, Karin M. Frei4, Paula J. Reimer1

1 School of the Natural and Built Environment, Queen’s University Belfast, Elmwood Avenue, Belfast, Northern Ireland BT7 1NN, UK.2 UCD School of Earth Sciences and UCD Earth Institute, University College Dublin, Belfield, Dublin 4, Ireland.3 Irish Centre for Research in Applied Geosciences (iCRAG), Belfield, Dublin 4, Ireland.4 National Museum of Denmark, Environmental Archaeology and Materials Science, I.C., Modewegsvej, Brede, Kongens Lyngby 2800, Denmark.5 Present address: Archéozoologie, archéobotanique: sociétés, pratiques et environnements (AASPE UMR 7209), Muséum national d‘Histoire naturelle, CNRS, 55 rue Buffon, F-75231 Paris cedex 05, France.6 Corresponding author ([email protected]).

ABSTRACTThe Limfjord in Denmark held a prominent position throughout Prehistory as a natural com-munication port between east and west. Identifying the presence of non-local individuals might shed light on socio-economic and cultural changes occurring in the Limfjord area. Existing studies attempting to do so using strontium isotope analysis on Danish prehistoric remains focus on certain archaeological time periods and/or geographic locations, resulting in an uneven distribution of analysed material. This study aimed at filling a gap in the existing literature, both from a geographical as well as a chronological point of view. Additionally, carbon and nitrogen stable isotope analysis on bone and tooth dentine from these individuals was carried out to examine dietary changes between childhood and adulthood. The strontium isotope results revealed that three, potentially four, out of 27 individuals fall outside the “local” bioavailable baseline range; two from the Neolithic, one from the Early Roman Iron Age and one from the Germanic Iron/Viking Age. We conducted incremental stable isotope analysis of tooth dentine from the three, potentially four, non-local individuals to investigate the palaeo-dietary information in their dental records at a higher resolution and potentially pinpoint their age at the time of movement. The two Neolithic individuals revealed stable isotope ratios that might be indicative of stress.

ARTICLE HISTORYReceived 11 October 2019;Accepted 16 April 2020

KEYWORDSStrontium isotopes; Stable isotope analysis; Mobility; Denmark; Limfjord.

2 Laura G. van der Sluis et al.

2018; Frei et al., 2019). From within Scandina-via, Denmark has yielded the highest number of strontium isotope investigations. However, as in many other areas, the current literature does not equally represent all prehistoric periods. In Den-mark, the two periods that seem to be mostly rep-resented are the Bronze Age and the Viking Age.

In this paper we will attempt to identify mi-grants using strontium isotope analysis on hu-

man remains from the Limfjord area. This study aims to contribute to filling in this gap in Danish strontium isotope studies in two ways:

1) by providing new strontium isotope data from the Limfjord area –an area that has not yet been much investigated-, and 2) by providing strontium isotope data from various prehistoric periods, thus filling a chron-ological gap.

Besides measuring strontium isotopes in human enamel, we measured strontium concentrations with the aim to discuss its potential value as an additional proxy. Additionally, the combination of strontium isotope analysis on the tooth enam-el and carbon and nitrogen stable isotope analy-sis on the tooth dentine from the same tooth is also discussed. Finally, we performed incremental dentine carbon and nitrogen stable isotope anal-ysis on a selection of teeth to investigate dietary changes during childhood and examine if a change in residency of an individual could potentially be linked to a change in diet from which the age of the movement could be deduced.

Figure 1. ArcGIS map with the sample numbers used in this study from the Limfjord area. The location of the Limfjord in Denmark is displayed in the inset. Used with permission (Copyright © 2017 Esri, ArcGIS Online, and the GIS User Com-munity. All rights reserved).

Figure 2. Timetable of Danish prehistoric periods.

cal AD 800-1050 Viking Age (VK)

cal AD 400-800 Germanic Iron Age (GER)

0 cal BC/AD–cal AD 400 Roman Iron Age (RIA)

500 cal BC–0 cal BC/AD Pre-Roman Iron Age (PRIA)

1000-500 cal BC Late Bronze age (LBA)

1700-1000 cal BC Early Bronze Age (EBA)

2400-1700 cal BC Late Neolithic (LN)

2800-2400 cal BC Middle Neolithic B (SGK)

3300-2800 cal BC Middle Neolithic A (MN)

3900-3300 cal BC Early Neolithic (EN)

5400-3900 cal BC Late Neolithic – Ertebølle (ERT)


2. Movement of people in Danish prehi-story

During the Neolithic small groups of people or in-dividuals with farming skills have been assumed to have migrated into Denmark, probably spreading their knowledge to the local population (Sørensen and Karg 2014). The difference in pottery tech-nique (Jensen 2013), the discrepancy between Scandinavia’s wild aurochs and domesticated cattle (Noe-Nygaard and Hede 2006) and the relatively fast adoption of farming during the Neolithic all seem to suggest that migrants played an important role in the Mesolithic-Neolithic transition in Scan-dinavia. This is supported by ancient DNA studies, which reveal that Scandinavian farmers shared a closer genetic affinity with Central European farm-ers than with Mesolithic hunter-gatherers (Malm-ström et al., 2009; 2015). Additionally, numerous Bell Beaker potteries from the Late Neolithic pe-riod have been found around Limfjord, suggest-ing the existence of connections with Bell Beaker groups in central Europe (Arthursson 2015). These connections potentially enabled metal to be circu-lated to the North. Strontium isotope analyses also showed that Bell Beaker individuals from central Europe had a high degree of mobility (Price et al., 2004). However, recent investigations suggest that the distribution of Bell Beaker communities was spread out over Europe in seemingly isolated is-lands, although similarities in their material culture suggest that a degree of human mobility was in-volved (Vander Linden 2015). More recently, Frei et al. (2019) analysed strontium isotope ratios on human remains of 88 individuals from Denmark in order to investigate the degree of mobility across the Neolithic-Bronze Age transition. Four of these 88 individuals with radiocarbon ages dating to the Neolithic were excavated from the Limfjord area (2x Sejerslev, Dommergården and Sebber skole). Their strontium isotope ratios fall within the “lo-cal” baseline range for present-day Denmark.

During the Bronze Age the emergence of a su-pra-regional network which connected faraway regions, is evident in southern Scandinavia and northern Germany (Price et al., 2017; Berger-brant et al., 2017; Frei et al., 2015a; Frei et al., 2017; Frei et al., 2019). During this period, mo-

bility seems to have involved warriors (Price et al., 2017), commoners (Bergerbrant et al., 2017) and even elite females (Frei et al., 2015a; Frei et al., 2017). Due to the emergence of a social elite and the development of chieftains who presumably controlled the trade, warriors might have become indispensable for the protection and regulation of such a complex network (e.g. Kristiansen and Earle 2015). The Danish Jutland peninsula, in which Limfjord is situated, obtained a prominent position in the trading network from around the beginning of the Early Bronze Age (between 1700-1600 BC) onwards, probably due to the trade of metal and amber (Kristiansen 1987; Kristiansen and Larsson 2005; Nørgaard et al., 2019). Hu-man mobility during the Nordic Bronze Age has also been illustrated by Frei et al. (2019) who ob-served a change in human mobility patterns from around 1600 BC. This change, which seems to have occurred during the transition period at the beginning of the Nordic Bronze Age, a time when society flourished, expanded and experienced an unprecedented economic growth, suggests that trade and human mobility might have been close-ly related. Two (Jestrup, and Øster Herup) out of 14 Bronze Age individuals analysed from the Lim-fjord area yielded non-local Sr isotopic signatures (Frei et al., 2019).

After the collapse of the interregional trading net-work and the associated hierarchical society at the end of the Bronze Age, the Pre-Roman Iron Age in Scandinavia seems to become more egalitarian (Myhre 2003). This is evident from cremation bur-ials which at this time appear to be uniform and without rich furnishings (Sellevold et al., 1984; Myhre 2003). Additionally, this period reveals an intensification of the farming system in the form of Celtic fields, which enabled more reliable crop rotation systems. Overexploitation of resources towards the end of the Bronze Age provided an opportunity for technological innovations, which were essential during the Iron Age; farming be-came possible on heavy soils, while iron could be extracted locally in many places in Denmark, giv-ing the local communities more independence and reducing their need for long-distance trade (Kris-tiansen 2010). The focus on locally available metal raw materials and the collapse of the Bronze Age


network would suggest that people were less mo-bile during the Pre-Roman Iron Age compared to the previous period.

The Roman Iron Age was characterised by a re-opening up and increasing contact between Germanic tribes and Romans, resulting in trading and raiding activities. Defensive mechanisms, i.e., earthworks and fortifications, were constructed throughout the landscape in an attempt to with-stand invasions (Kaul 1997, 2003; Jensen 2013). Archaeological evidence suggests several attacks against southern Scandinavia occurred, coincid-ing with the deposition of substantial offerings of weapons and riding gear (Ilkjær 2000). The chief-dom-oriented society that emerged during the Late Roman period continued into the German-ic Iron Age (Hall 2007). In addition to raids and attacks, market towns emerged in the 8th century and offered people the opportunity to gain per-sonal wealth for maintaining prestige and securing alliances with other military leaders (Hall 2007).

The Viking Age is well known for its colonisations and long distance travel (Hall 2007). Market plac-es developed into small towns with administrative, religious and legal activities in addition to trad-ing and commerce (Hall 2007; Skre 2008; Jensen 2013; Price 2015; Ashby et al., 2015). In Denmark, several Viking Age sites have been investigated us-ing strontium isotopic analyses of human remains, including the Limfjord site of Sebbersund, where three out of 19 analysed individuals have been identified as non-local (Price et al., 2012). Howev-er, this site has yielded more than 700 individuals, hence it is not possible at this point to estimate the percentage of non-locals vs. locals at this site.

At the Viking Age site of Galgedil on the island of Funen, tooth enamel samples from 36 humans yielded non-local Sr isotope values, which is about a third of the dataset (Price et al., 2015). Finally, Sr isotopic data from the famous fortress of King Harald Bluetooth, Trelleborg on the island of Zea-land, indicated an even higher number of non-lo-cals (Price et al., 2011; Frei et al., 2014).

3. Strontium isotope analysis

Strontium isotope analysis has proven to be a use-ful tool in identifying non-local individuals with-in the Scandinavian realm (Sjögren et al., 2009; Frei et al., 2015a; 2015b; Price et al., 2015; 2017; Bergerbrant et al., 2017; Frei et al., 2019). Geo-graphical movements can be identified by com-paring 87Sr/86Sr isotope ratios from tooth enamel with the local bioavailable 87Sr/86Sr isotopic range, which relates to the underlying geology (Eric-son 1985; Price et al., 2002; Bentley 2006; Frei et al., 2020). After strontium is taken up into the human body through food and drinking water, it is incorporated into the mineral lattice of hy-droxyapatite by substituting for calcium (Bentley 2006; Katzenberg 2008). However, a migrant will only become visible if the recorded 87Sr/86Sr ra-tio in human tissues deviates sufficiently from the local 87Sr/86Sr isotopic range. An individual travelling between two or more regions with the similar 87Sr/86Sr ranges might appear to be local. Similarly, a young individual whose tooth enamel is still forming, travelling across regions with vary-ing 87Sr/86Sr ranges will present an average value of all of these strontium sources. Additionally, large and continuous marine food consumption during childhood can affect the tooth enamel 87Sr/86Sr values, pulling them towards the marine isotopic signal (Price and Naumann 2015). As the modern sea water 87Sr/86Sr signal falls within the Danish 87Sr/86Sr baseline, these individuals would appear local while they might not be, providing a conserv-ative number of migrants in the dataset.

3.1 Diagenesis

Due to the high mineral content (Fitzgerald and Rose 2008), increased crystallographic organisation, crystal size and extremely low porosity, tooth enamel is less susceptible to diagenesis than dentine (Bent-ley 2006). Dentine is similar to bone in terms of composition and crystal size, although it is less po-rous than bone (Hillson 2005; Koch 2007; Burton 2008). Diagenesis should be taken into considera-tion when dealing with Sr isotopic data from den-tine. Uptake of Sr from the burial environment in-cluding soil pore fluids by relatively porous dentine


would likely result in convergence of the dentine Sr isotopic composition towards the values in the soil, assuming that the latter acts as an infinite reservoir.

3.2 Geology and Sr isotope geochemistry of Denmark

Compared to northern Scandinavian countries, Denmark is geologically relatively young. The geo-logical bedrock consists among others of Late Cre-taceous/Early Cenozoic carbonate rocks and ma-rine clastic sediments, while the surface is overlain by glaciogenic sediments containing weathered Precambrian material originating from Norway and Sweden (Frei and Frei 2011; Frei and Price 2012). The Danish soil surface is composed of gla-cially transported reworked basement material and local deposited sediments (Frei and Price 2012; Houmark-Nielsen and Kjær 2003). While the limestone ranges in 87Sr/86Sr values between 0.7078 and 0.7082, the glaciogenic tills have more radio-genic values (87Sr/86Sr >~ 0.7095) (Frei and Frei 2011). The Limfjord region is characterised pre-dominant by Upper Cretaceous to Lower Tertiary carbonates with outcrops of Eocene and Oligocene volcanic ash layers. Both types of lithologies exhib-it unradiogenic strontium isotopic values which seem to have influenced the 87Sr/86Sr ratios of local surface waters (Frei and Frei 2011). The bioavail-able strontium isotopic range of present-day Den-mark (87Sr/86Sr = 0.7081 - 0.7111; excluding the Danish island of Bornholm, southeast of Sweden) was originally estimated from analysis of surface waters (Frei 2013; Frei and Frei 2011). These data have since been supplemented by analyses of envi-ronmental samples including soil extracts, plants, surface waters and fauna samples (e.g. Hoogewerff et al., 2019, Frei et al., 2017, Price et al., 2012, Price et al., 2011; Reiter et al., 2019; Frei et al., 2020), which have confirmed the range based on the surface waters alone.

4. Carbon and nitrogen stable isotope analysis

Carbon and nitrogen stable isotope data are com-monly used in palaeodietary studies. For both car-

bon and nitrogen, uptake of the heavier isotopes increases with trophic level, ~1 ‰ for δ13C (De-Niro and Epstein 1978) and ~3 ‰ for δ15N (De-Niro and Epstein 1981), although higher enrich-ments have also been reported (~3-4‰) (Hedges and Reynard 2007). δ13C values are useful in dif-ferentiating between terrestrial C3 plants (Smith and Epstein 1971; Price et al., 1985) and marine vegetation (DeNiro and Epstein 1978) in Prehis-toric Denmark. A nursing effect can raise δ15N values in breastfeeding children (Fogel et al., 1989; Richards et al., 2002). Stable isotope analysis per-formed on adult human bone gives an indication of the consumed diet of an individual’s last years in life (depending on the bone element and its relat-ed remodelling time (Cox and Sealy 1997; Jørkov et al., 2009) prior to death. Because tooth enamel and the primary dentine are formed during child-hood and do not remodel after formation, these tissues record and preserve isotopic information from childhood (Piesco 2002; Garg and Garg 2013; Nanci 2013), making them exceptionally suitable for studies involving migration. While the strontium isotope analysis of the tooth min-eral can reveal a potential change in residency, the corresponding tooth dentine can provide informa-tion about the diet during childhood and changes therein.

5. Material

Tooth enamel and bones samples were select-ed based on preservation and availability, from a larger set of human and faunal samples collected from Danish museums for a large-scale palaeodi-etary study (van der Sluis 2017). As such, the lo-cations of the tooth enamel samples in this study are spread around the Limfjord area, both in a ge-ographical as well as in a chronological sense. The current dataset is largely composed of single finds originating from the Neolithic to the Viking Age. In total 27 human (Table 1) and 9 faunal (Table 2) tooth samples from the Limfjord in Denmark were analysed. All human teeth had fully developed roots, characterised by apical closure, except for two samples, Øslev (Lim-ht-054) and Romb (Lim-ht-061). The latter had incomplete roots, which were finished to stage R ¾, indicating an age of


Tooth sam-ple number

Tooth code

Location Bone sample number

Bone element

Sex/age Museum number

AS_ID and/or grave number

Archaeological period

Remarks

Lim-ht-054 7- Øslev Lim-hb-095 femur fragment

ÅHM 1128/59 23/60 Single Neolithic

Lim-ht-055 7- Torsholm Lim-hb-049 mandible (powder)

juvenile NM A38203 Individual A Neolithic

Lim-ht-056 -7 Torsholm Lim-hb-048 mandible (powder)

juvenile 16-17 years

NM A38203 Individual B Neolithic

Lim-ht-057 5 Krejbjerg og Ginderup

Lim-hb-044 mandible NM A26287-99

Individual 1 Early/Middle Neolithic

Lim-ht-058 5+ Krejbjerg og Ginderup

Lim-hb-045 cranium (powder)

NM A26287-99

Individual 2 Neolithic

Lim-ht-059 -6 Bjørnsholm (Vitskøl)

Lim-hb-004 long bone fragment

NM 1107/57 08/58 Middle Neo-lithic/SGK

Lim-ht-062 6+ Færkerhede Lim-hb-005 humerus female? 18-20 years

NM 512/55 18/81 Late Neolithic M3 was erupting

Lim-ht-190 4+ Lodbjerg klit Lim-hb-146 cranium female? adult THY 6165 x1 Early Middle Neolithic

only enamel

Lim-ht-191 7 Møgelvang Lim-hb-148 cranium THY 2151 x300 Neolithic

Lim-ht-192 -6 Højvang Mark Lim-hb-153 femur THY 1098 x19 Single Neolithic

Lim-ht-193 7+ Næsby Østergård

Lim-hb-182 cranium fragments

20-25 years VMÅ 2251 x8 grave A2 Late Neolithic only enamel

Lim-ht-060 6- Nørtorp Lim-hb-024 humerus male 40-50 years

NM 909/59 4/59 skeleton #1

Early Bronze Age

Lim-ht-063 +6 Følhøj Lim-hb-042 mandible (powder)

18-21 years NM B10830-32

Early Bronze Age

M3 was erupting

Lim-ht-064 -8 Rærgård x female 30-40 years

NM 576/12 B9653-54

Early Bronze Age

Only tooth, no bone

Lim-ht-189 6 Nørhå Lim-hb-138 fibula female 18-35 years

THY 1550 x13 (bone) x13B1 (tooth)

Early Bronze Age

Lim-ht-065 4 Nørre Trand-ers Præstegård

Lim-hb-107 femur male adult ÅHM 42/55 skeleton 1 Early Roman Iron Age

Lim-ht-066 6- Nørre Trand-ers grusgrav

Lim-hb-112 tibia female 55-60 years

ÅHM 16/58 Grave 5 Early Roman Iron Age

very mature

Lim-ht-068 5+ Christianshøj (Romdrup)

Lim-hb-113 cranium fragment

male adult ÅHM 20, 4578-81

45/55 skele-ton 1

Early Roman Iron Age

underneath stone layer

Lim-ht-070 -7 Korsø Lim-hb-019 cranium (powder)

adult male NM 560/59 7/59 Grave III Early Roman Iron Age

Lim-ht-072 +6 Rygegård Lim-hb-105 long bone fragment

male 30-50 years

ÅHM 1469x4 20/85 Early Roman Iron Age

Lim-ht-071 -7 Vandet skole Lim-hb-036 ulna adult, possibly male

NM 925/59 3/60 Grave 1 Late Roman Iron Age

very rich grave

Lim-ht-073 -5 Klim Lim-hb-017 femur female adult NM C27382-400, 1167/57

13/58 Late Roman Iron Age

very rich grave

Lim-ht-074 -5 Gammel Hasseris

Lim-hb-006 femur female mature NM 759/61 8-64 Grave 1 Late Roman Iron Age

rich grave

Lim-ht-061 +6 Romb Lim-hb-031 cranium fragment

adult 20±2 years

NM B10706 Grave C Germanic/Vi-king Age

Lim-ht-079 4- Aggersborg Kirke

Lim-hb-001 ulna male 20-35 years

NM D1916/1977

13/81 Viking Age 1030 AD (14C dated)

Lim-ht-080 -5 Brårup Lim-hb-022 cranium fragment

male adult NM C28826-29, 477/61-62

14/69 skele-ton 1

Viking Age

Lim-ht-081 7+ Sebbersund Lim-hb-087 cranium fragment

female 18-35 years

ÅHM 2863 32/02 x398 F4676

Viking Age F number (Price et al.,

2012)Lim-ht-194 7 Næsby Lim-hb-187 rib frag-

mentsprobable female

VMÅ 867 Grave A124 box A x497

(bone) box V x1153 (tooth)

Viking Age rich female chamber

grave, only enamel

Table 1. Material obtained from human remains used in this study. The tooth code refers to the number of the tooth ele-ment counted from the first incisor (1-8), + refers to a maxillary and – to a mandibular element, while the side is indicated by whether the + or – stands on the left or right of the element number. For example, +4 refers to the left maxillary 1st pre-molar. Age and sex where identified was possible are as reported in the original reports. *Strontium isotope analysis was performed by Price et al. (2012) on the Sebbersund sample (Lim-ht-081). This sample was included here for measuring the δ13C and δ15N values of the bone and dentine collagen.


7 ± 0.5 years (Moorrees et al., 1963; AlQahtani et al., 2010). The roots of the tooth from Øslev were broken off, presenting roots up to formation stage of R ½, corresponding to an age of circa 10.5 ± 0.5 years of age (Moorrees et al., 1963; AlQahtani et al., 2010). Skeletal remains of 13 human individ-uals were subjected to radiocarbon dating (Appen-dix 2), which was performed on the bone collagen from same individual.

6. Method

Methods of strontium isotope analysis, carried out in two laboratories are described, as well as meth-ods for bone and incremental dentine collagen ex-traction.

6.1 Strontium isotope analysis

Tooth enamel samples weighed between 1.35 to 31.82 mg, with the small faunal samples providing the smaller amounts of tooth enamel. Two sam-ples were analysed in both laboratories to test for tooth enamel heterogeneity, which involved taking two different enamel pieces from the same tooth. Human tooth enamel of 12 individuals were ana-lysed at the University of Copenhagen, Denmark. Tooth enamel samples were cleaned and cut using a diamond dental burr. Any remaining dentine was carefully removed with the dental burr. The drilling equipment was thoroughly cleaned between sam-ples with weak HCl acid (Seastar). After placing samples in pre-cleaned and numbered 7 mL Teflon (Savillex™) beakers, 6 drops of 30 % H2O2 (Seastar) and 3 drops of 6N HCl (Seastar) were added. The

Teflon beakers were placed on the hotplate to dis-solve the samples (few minutes), after which the lids were removed and samples left to dry at 80 °C. Subsequently, the enamel samples were taken up in a few drops of 3N HNO3 and loaded onto dis-posable 100 µl pipette tip extraction columns into which we fitted a frit which retained 0.2 mL stem volume of intensively pre-cleaned mesh 50-100 Sr-Spec™ (Eichrome Inc.) chromatographic resin. The elution recipe essentially followed that by Horwitz et al. (1992), albeit scaled to our needs in so far as strontium was eluted by deionised water and then the eluate placed on the hotplate at 80 °C until dry. Thermal Ionisation mass spectrometry (TIMS) was used to determine the Sr isotope ratios. Samples were dissolved in 2.5 µl of a Ta2O5-H3PO4-HF ac-tivator solution and directly loaded onto previously outgassed 99.98 % single rhenium filaments. Sam-ples were measured at 1250-1300 °C in dynamic multi-collection mode on a VG Sector 54 IT mass spectrometer equipped with eight faraday detectors (Institute of Geosciences and Natural Resource Management, University of Copenhagen). Five na-nogram loads of the NBS 987 Sr standard that we ran during the time of the project yielded 87Sr/86Sr = 0.710241 ± 0.000011 (n=5, 2σ).

The other strontium isotope measurements were analysed at the National Centre for Isotope Ge-ochemistry (NCIG) at UCD School of Earth Sciences, University College Dublin, Ireland. In total 30 measurements were made at UCD, three of which were on dentine, the rest on enamel. Of these 27 enamel samples, two were repeats (Lim-ht-061 and Lim-ht-066) of the samples analysed in Copenhagen to test for tooth enamel heterogenei-ty. One sample was analysed twice at UCD due to

Tooth sample Animal species Location Museum ID number Archaeological period

Lim-at-330 Equus caballus Kammerhøj ved Redsted Mors museum Viking Age

Lim-at-331 Microtis Aggersborg ZMK109/1948 x49/559 Viking Age

Lim-at-333 Mus sp. Hov, Flintmine ZMK115a/1957 Neolithic

Lim-at-335 Capreolus capreolus Krabbesholm II ZMK50/2000 A6325 early Neolithic

Lim-at-336 Cervus elaphus Krabbesholm II ZMK50/2000 4478 early Neolithic

Lim-at-337 Bos taurus Krabbesholm II ZMK50/2000 2879 early Neolithic

Lim-at-339 Cervus elaphus Kokkedalsmark ZMK64/1983 x15 Bronze Age

Lim-at-340 Microtis Mellemholm ZMK31/1979 x340 Pre-Roman Iron Age

Lim-at-343 Microtis Smedegård ZMK38/1993 x501 Iron Age

Table 2. Faunal material used in this study.


its highly radiogenic isotopic value (Lim-ht-191). Three dentine samples were analysed to examine the potential effect of diagenetic alteration on the 87Sr/86Sr values.

To cut enamel and dentine samples and clean the surface, dremel tools were used, which were thoroughly cleaned with weak HCl acid and Mil-li-Q water between taking samples. Samples were weighed into pre-cleaned Savillex Teflon beakers, dissolved in 2.5 mL of 6M HCl (aq.) and placed on the hotplate at 100 °C for evaporation. Samples were subsequently dissolved in 1 mL of concentrat-ed (69 %) HNO3 to breakdown any organics and evaporated at 100 °C. Columns were prepared us-ing pre-cleaned filter frits, which were cleaned in a sonic bath for 10 minutes and stored in 1M HNO3, while the Sr resin (Eichrom 100-150 µm) was measured by volume (20 mm from the bottom frit, equal to 100 mg). Columns were cleaned using sev-eral acid washes of 1M and 8M HNO3 to remove other trace elements, finishing with 1M HNO3 for preconditioning. Samples were dissolved in 1 mL of 1M HNO3, placed in centrifuge tubes and spun down at 5000 RPM for 30 minutes to remove any particulate matter that might otherwise block the resin. Samples were introduced to the columns, washed with 1M and 8M HNO3 to remove other trace elements, after which strontium is collected in pre-cleaned Teflon beakers using 2 mL 0.05M HNO3. Collected samples of strontium were evap-orated on the hotplate at 100 °C, dissolved in 1 mL concentrated HNO3 to remove any organics from the resin and evaporated again. Strontium samples were dissolved in 0.05M HNO3 and loaded onto rhenium filaments after which a tantalum-based activator (TaCl5) was added for analysis on the Tri-ton (TIMS). The average blank at UCD contained less than 1 ng of strontium, indicating a negligible amount of strontium contamination in the lab. During the period when the Limfjord analyses were run at UCD, the SRM987 reference material yield-ed 87Sr/86Sr = 0.7102611±0.0000144 (2σ, n = 19).

Although measurements of 87Sr/86Sr in the SRM987 reference material in both Copenhagen and Dublin fall within uncertainty of the nominal value, they deviate in opposite senses (-0.000009 ± 0.000011 in Copenhagen and +0.000011 ± 0.000014 in Dublin). Hence, all measurements reported in this study have been normalised to the

nominal value, i.e., 0.710250. Based on the repro-ducibility of analyses of SRM987 (in both Copenha-gen and Dublin), a global uncertainty of ±0.00001 (2 sigma) is used for all 87Sr/86Sr analyses reported in this study (Table 3).

Strontium aliquots were taken to determine the strontium concentrations (ppm) using the Neptune ICPMS. These aliquots were made up to ca. 3 % HNO3, and centrifuged to remove any particulate matter that could block the nebuliser. Sr concentra-tions are accurate to ca. 10 % and were calibrated using dilutions of the Ionex Multi Element ICP standard Solution 8E (Neptune Tune-up solution).

6.2 Bone and incremental dentine colla-gen extraction (IRMS) and radiocarbon dating (AMS)

The bone collagen extraction protocol (Brock et al., 2010) is based on the Longin method (Longin 1971) with the inclusion of an ultrafiltration step (Brown et al., 1988; Bronk Ramsey et al., 2004). A detailed description of the protocol, used stand-ards and standard error on measurements is given elsewhere (van der Sluis et al., 2018). Collagen ex-traction for incremental dentine analysis followed method 2 from Beaumont et al. (2013). Samples were analysed using the Thermo Delta V IRMS with Flash Elemental Analyzer at the 14CHRONO Centre in Belfast. Collagen samples were combust-ed, graphitised and run in the NEC compact model 0.5MV AMS at the 14CHRONO Centre in Belfast (Appendix 2).

7. Results

Strontium isotope and strontium concentration results are presented first followed by the tooth dentine, bone collagen and incremental dentine collagen results.

7.1 Strontium isotope results

In total 87Sr/86Sr ratios were measured in 36 tooth enamel samples, of which 27 were human samples and nine were fauna samples (Table 3). The stron-


Sample Site name Archaeological period 87Sr/86Sr1 Sr (ppm)Lim-ht-054 Øslev Late Neolithic 0.70934Lim-ht-056 Torsholm-individual B Early Neolithic 0.71023Lim-ht-059 Bjørnsholm Vitskøl Neolithic 0.71013Lim-ht-060 Nørtorp #1 Early Bronze Age 0.70913Lim-ht-062 Færkæde AS 18/81 Late Neolithic 0.70931Lim-ht-063 Følhøj Early Bronze Age 0.71004Lim-ht-064 Rærgård Early Bronze Age 0.70998Lim-ht-065 Nørre Tranders Præstegård Early Roman Iron Age 0.70907Lim-ht-070 Korsø Early Roman Iron Age 0.71021Lim-ht-071 Vandetskole grav 1 Late Roman Iron Age 0.70958Lim-ht-061* Romb Germanic/Viking Age 0.71187Lim-ht-066* Nørre Tranders SOR grusgrav Grav 5 Early Roman Iron Age 0.70883Lim-ht-061* Romb Germanic/Viking Age 0.71203 130Lim-ht-066* Nørre Tranders SOR grusgrav Grav 5 Early Roman Iron Age 0.70884 127Lim-ht-055 Torsholm -individual A Early Neolithic 0.70995 63Lim-ht-057 Krejbjerg og Ginderup E/M Neolithic 0.71137 101

Lim-ht-057d Krejbjerg og Ginderup dentine E/M Neolithic 0.71441 116Lim-ht-058 Krejbjerg og Ginderup SGK Neolithic 0.71100 90

Lim-ht-058d Krejbjerg og Ginderup dentine SGK Neolithic 0.71427 104Lim-ht-068 Christianshøj (Romdrup) Early Roman Iron Age 0.70826 41Lim-ht-072 Rygegård Early Roman Iron Age 0.71111 70Lim-ht-073 Klim Late Roman Iron Age 0.71095 67Lim-ht-074 Gammel Hasseris Late Roman Iron Age 0.70996 60Lim-ht-079 Aggersborg Kirke Viking Age 0.71074 69Lim-ht-080 Braarup Viking Age 0.71029 218Lim-ht-189 Nørhå Early Bronze Age 0.71045 67Lim-ht-190 Lodbjerg klit Neolithic 0.70983 63Lim-ht-191* Møgelvang SGK Neolithic 0.71387 188Lim-ht-191* Møgelvang SGK Neolithic 0.71383 122Lim-ht-191d Møgelvang dentine SGK Neolithic 0.71123 218Lim-ht-192 Højvang Mark SGK Neolithic 0.70883 91Lim-ht-193 Næsby Østergård Late Neolithic 0.71003 156Lim-ht-194 Næsby Viking Age 0.71006 177Lim-at-330 horse Kammerhøj ved Redsted Viking Age 0.71042 446Lim-at-331 vole Aggersborg Viking Age 0.70909 398Lim-at-333 mouse Hov, Flintmine Neolithic 0.70828 260Lim-at-335 deer Krabbesholm II Early Neolithic 0.71069 303Lim-at-336 deer Krabbesholm II Early Neolithic 0.71080 209Lim-at-337 cattle Krabbesholm II Early Neolithic 0.70992 326Lim-at-339 deer Kokkedalsmark Bronze Age 0,71077 290Lim-at-340 vole Mellemholm Pre-Roman Iron Age 0.70841 478Lim-at-343 vole Smedegård Iron Age 0.70914 326

1: All analyses have been normalised to a 87Sr/86Sr value = 0.71025 for the SRM 987 reference material (see text).

*Samples analysed in CPH and UCD to test sample heterogeneity.

Table 3. 87Sr/86Sr ratios (TIMS) and strontium concentration (ICPMS) of human tooth enamel and dentine (“d” in the samp-le number) and animal tooth enamel samples. The first 12 samples were analysed at Copenhagen and lack the strontium concentration data.


tium isotope ratios from our samples of human re-mains range from 0.70826±0.00001 (Lim-ht-068 measured in tooth enamel) to 0.71441±0.00001 (Lim-ht-057d measured in dentine). Two sam-ples were analysed in both laboratories to test for tooth enamel heterogeneity. Sample Lim-ht-066 produced a 87Sr/86Sr ratio of 0.70884 ± 0.00001 in UCD and 0.70883 ± 0.00001 in Copenha-gen, showing no detectable heterogeneity within analytical reproducibility. However, some samples display varying degrees of heterogeneity. For ex-ample, sample Lim-ht-191 yielded 87Sr/86Sr values of 0.71387 ± 0.00001 and 0.71383 ± 0.00001 in UCD. This small difference is potentially due to tooth enamel heterogeneity, which is supported by their different Sr concentrations. Sample Lim-ht-061 yielded a slightly larger difference ranging from 87Sr/86Sr = 0.71203 ± 0.00001 in UCD to 0.71187 ± 0.00001 in Copenhagen, suggesting a larger sample heterogeneity. This difference could stem from intra-sample variability related to dif-ferent areas in the tooth from which the enamel samples was taken, which could be linked to a change in diet or perhaps a change in residency. As human tooth enamel formation takes several years to complete (AlQahtani et al., 2010), enamel from the crown can produce a different strontium iso-topic signal than enamel closer to the root, in case this individual was geographically mobile during the time of formation.

While sample Lim-ht-072 (Early Roman Iron Age) is very close to the boundary of the baseline, samples with more radiogenic values (Lim-ht-057 (Neolithic), Lim-ht-061 (Germanic/Viking Age) and Lim-ht-191 (Neolithic)) indicate non-local individuals (Figure 3). The voles and mouse dis-play similar 87Sr/86Sr ratios, while the large herbi-vores show more radiogenic isotopic values (Fig-ure 3), which is probably related to the difference in feeding behaviour. Still, all animals from this study display 87Sr/86Sr ratios that fall within the Danish baseline of 87Sr/86Sr = 0.7081 and 0.7111. As such, our 87Sr/86Sr ratios of the faunal samples correspond well with the existing Danish baseline. However, a recent publication aiming at propos-ing a standardisation of how to create bioavailable strontium isotope baselines, recommends not to use animals, as even mice have been shown not to be local (Grimstead et al., 2017). Hence these should still be considered with care.

Our faunal tooth enamel samples have relatively high strontium concentrations (209-478 ppm, Table 3) in keeping with the general pattern that, compared with carnivores, herbivores have higher Sr concentrations in their tissues because plants are rich in strontium while meat is low in strontium (Bocherens et al., 1994; Tuross et al., 1989; Mont-gomery 2010). Strontium concentration values be-tween 50-300 ppm have been reported in modern

Figure 3. 87Sr/86Sr ratios and Sr concentra-tions of human and animal teeth from the Limfjord study. Samples displayed on the y-axis are the 12 samples lacking Sr con-centration data and have been arbitrarily set to zero. 87Sr/86Sr ratios from samples Lim-ht-061 and Lim-ht-066 are plotted twi-ce since two subsamples from each have been analysed. The area between the black lines represents the Danish baseline (87Sr/86Sr = 0.7081 to 0.7111) (Frei and Frei 2011).


human skeletal and dental tissues (Brudevold and Söremark 1967; Elliott and Grime 1993; Han-cock et al., 1989; Underwood 1977; Montgomery 2010) in keeping with our human tooth enamel data from the Limfjord (41-218 ppm, Table 3).

Three dentine samples were analysed to examine the potential effect of diagenetic alteration on the 87Sr/86Sr values. This is evident in sample Lim-ht-191 (Figure 4), whose enamel is much more radiogenic (87Sr/86Sr = 0.71387) than its den-tine (87Sr/86Sr = 0.71123). However, the other two samples (lim-ht-057 and Lim-ht-058) show the opposite trend, i.e., their dentine is more radiogenic (Figure 4). There are several possible explanations for this. Firstly, as dentine repre-sents a different formation period than enamel, the difference could potentially indicate mobil-ity between the formation of these two tissues. Alternatively, the burial environment may have masked the original strontium values as a result of diagenesis. Finally, it can also be a combination of these factors.

The availability of Sr concentration data for most of the samples permits possible mixtures of Sr sourc-es to be evaluated, at least qualitatively (Figure 5). Frei and Frei (2011) observed a mixing line in their surface water samples between a possibly pre-Qua-ternary limestone source (low 87Sr/86Sr ratios and high Sr concentration) and a source in glaciogen-

ic soils, characterised by more radiogenic 87Sr/86Sr and low Sr concentration. Data in Figure 5 sug-gests a heterogeneous mixing scenario to explain the enamel and dentine data in our study. The pat-tern is similar to the one of Montgomery et al., (2007) for Neolithic and Bronze Age tooth enamel samples from England. In their study, Montgom-ery et al. (2007) suggest that this pattern is due to variable mixtures of more than two sources similar to data from the Neolithic individuals in the York-shire study of Montgomery et al., (2007). Two of the extreme end members in our study seem to be characterized by: 1) high Sr isotopic compositions and high Sr concentrations (low 1/Sr values); 2) intermediate Sr isotopic compositions and low Sr concentrations (higher 1/Sr values), indicated by respective trend arrows in figure 5. The third and common end member is characterized by low Sr isotopic compositions and high Sr concentrations which we equate with limestones also inferred by the study of Montgomery et al., (2007). This could indicate more than two endmembers are contrib-uting strontium and/or that people were exploit-ing a variety of food sources.

7.2 Tooth dentine and bone collagen sta-ble isotope results

One dentine increment from each tooth was an-alysed for its δ13C and δ15N ratios (Appendix 1).

Figure 4. 87Sr/86Sr ratios and Sr concent-rations of the faunal tooth enamel samples and human tooth dentine and correspon-ding enamel samples. The arrows point from the enamel to the dentine signal. Faunal samples from around the Limfjord area from Frei and Price (2012) have been added for comparison. Strontium concent-rations are not available for these samples and have been arbitrarily set to zero.


Dentine increments selected for stable isotope analysis were taken from the roots rather than the crown to avoid the influence of a weaning signal. As such, the post-weaning early childhood diet can be compared with the adult dietary signal from the same individual. Increments of all 27 teeth yield-ed acceptable C:N ratios (DeNiro 1985), except for one sample, Øslev 5 (Lim-ht-054), which was excluded from further analyses. All dentine results have corresponding bone collagen results from the same individual, except for Rærgård (Lim-ht-064), for which no bone sample was obtained. No den-tine was available from Lim-ht-193 and Lim-ht-194 and the corresponding bone samples failed to produce a signal on the IRMS. The change in diet is illustrated for each individual with an ar-row from the childhood diet (represented by the dentine sample) to the adult diet (represented by the bone sample) (Figure 6). These changes in diet can be interesting when combined with strontium isotope analysis to investigate a person’s geograph-ic origin. Large shifts in diet between the child-hood and adult life could indicate dietary changes related to different cultural practices or perhaps a change in residency.

Only changes in δ13C and δ15N ratios larger than 1‰ are discussed here. The Neolithic samples (Figure 6A) reveal four individuals with changes in at least one of their stable isotope ratios between adulthood and childhood. Sample Lim-ht-055 is

the only Neolithic sample that shows a decrease in both stable isotope ratios (1.4 ‰ in δ13C, 1.2 in δ15N) from the childhood diet to the adult diet. Three other samples reveal a change in one of their stable isotopic ratios - a drop in the δ15N ratios of 1.4 ‰ (Lim-ht-056), an increase in the δ15N ratio of 1.5 ‰ (Lim-ht-191) and an increase in the δ13C ratio of 1.1 ‰ (Lim-ht-057). The sam-ples from the Bronze Age show little variation be-tween the childhood and adult diets (Figure 6B), as do the samples from the Early Roman Iron Age (Figure 6C). The Late Roman Iron Age individuals seem to have different childhood diets but cluster around similar stable isotope ratios later in life, indicating a similar diet isotopically (Figure 6D). Sample Lim-ht-073 shows an increase in the δ13C ratio of 1.1 ‰ combined with a decrease in the δ15N ratio of 1.2 ‰ from the childhood diet to the adult diet. Sample Lim-ht-074 similarly reveals a drop in its δ15N ratio of 1.5 ‰. Two Viking Age samples show a decrease in both stable isotope ra-tios from the childhood to adulthood (Figure 6E), in Lim-ht-061 (1.2 ‰ in δ13C, 1.1 in δ15N) and Lim-ht-081 (1 ‰ in δ13C, 1 ‰ in δ15N).

An increase in δ15N ratios is visible from the Neolithic (8-10 ‰) to the Viking Age (~11-13 ‰), which is similarly visible in a large bone collagen stable isotope dataset from these prehis-toric periods and can be interpreted as the increase of marine protein consumption combined with a potential manuring effect (van der Sluis 2017).

Figure 5. 87Sr/86Sr ratios and Sr concen-trations of enamel and dentine samples analysed at UCD. The data array can be explained by contribution of strontium from three potential sources, each with their own strontium concentrations and stron-tium isotopic compositions. Trend arrows labelled 1 and 2 depict potential end-mem-bers of two of the sources, while limesto-nes constitute the third source characte-rized by high strontium concentrations and low strontium isotopic signatures. Individu-als interpreted as local are marked in red diamonds, while non-local individuals are plotted in black diamonds. Dentine values are plotted in yellow filled circles. Respecti-ve reference lines of the maximum Danish baseline (Frei and Frei, 2011) and modern sea water/rainwater are marked with black and blue dashed lines respectively.


Wider ranging δ13C and δ15N ratios are visible in Neolithic and Viking Age samples, while less var-iation is visible in samples from the Bronze Age and Roman Iron Age. The general trend in most time periods is one of decreasing δ13C and δ15N ratios from the dentine to the bone sample. While care was taken to avoid dentine increments likely to show a weaning effect, i.e. close to the crown, this cannot be ruled out completely as different weaning ages existed in different time periods. This decrease in δ13C and δ15N ratios most like-

ly indicates different diets were consumed during the childhood and adulthood, possibly connected to cultural practices regulating which food sources were available at certain ages. It is interesting to see more elevated isotopic ratios in the dentine than in the corresponding bone samples, suggesting these individuals were feeding on a higher trophic level in their early childhood (post-weaning) than in the final years of their adult life.

Figure 6. Tooth dentine and bone collagen δ13C and δ15N ratios from all prehistoric periods. Arrows indicate the change from childhood (tooth dentine) to adult (bone) diet. A: Neolithic. B: Bronze Age. The adult dietary (bone) signal is missing from Lim-ht-064 (Rærgård). C: Early Roman Iron Age. D: Late Roman Iron Age. E: Viking Age.


7.3 Incremental dentine stable isotope results

Stable isotope analysis was performed on incremen-tal tooth dentine sections from the 3, potentially 4, non-local individuals (Figure 7) to investigate their childhood diets and potentially connect this to their moment of movement. The two Neolithic teeth (Lim-ht-191 and Lim-ht-057) show a similar pattern with decreasing δ15N ratios combined with rising δ13C ratios from 3 to 8.5-9 years of age, af-ter which δ15N ratios start to rise combined with a slight decrease in δ13C ratios. The decrease in δ15N ratios in the early years could be related to the final phase of weaning, after which the child was most likely feeding on a low trophic level diet (e.g. por-ridge or gruel) with perhaps the addition of some low trophic level marine protein, considering the rise in δ13C ratios. However, the isotopic chang-es are rather large in Lim-ht-191, with a drop of 2.7 ‰ in δ15N ratios and a rise of 1.1 ‰ in δ13C ratios. The second half of the Neolithic profiles is characterised by increasing δ15N ratios, almost

2 ‰ in Lim-ht-191 and 1.5 ‰ in Lim-ht-057. In Lim-ht-191 the increase of almost 2 ‰ in δ15N is combined with a drop of 0.5 ‰ in δ13C. The bone collagen δ13C and δ15N ratios in both individuals are higher than their final dentine increments.

Interesting to note are the very low δ13C ratios (-21.8 ‰) in the early childhood of Lim-ht-191. It is possible that this individual lived in a forested en-vironment before consuming different food types.

The profile of Lim-ht-061 starts with a drop in δ15N ratios until the age of 3, possibly indicating a weaning remnant, followed by a rise of 2.5 ‰ in δ15N ratios and an increase of 0.4 ‰ in δ13C ratios. The co-variation between the two isotopic ratios would suggest diet as a factor for this shift, most likely the consumption of high trophic level marine protein. This individual is from the Ger-manic/Viking Age, a time period when the con-sumption of marine food sources is evident on a larger scale again (van der Sluis 2017). The bone collagen δ13C and δ15N ratios are considerably lower than the last dentine increment. If a change in residency can be associated with a change in sta-

Figure 7. Incremental tooth dentine profiles of δ13C and δ15N ratios for the four non-local individuals. Bone collagen δ13C and δ15N ratios are displayed at the far right of each graph by a marker with a black outline.


ble isotope ratios, it seems plausible that this oc-curred after the age of 7 for this individual.

In Lim-ht-072 breastfeeding possibly contin-ued until the age of 2, after which a slight decrease of 0.3‰ in δ15N ratios and increase of 0.7 ‰ in δ13C ratios is visible, followed by an elevation in δ15N ratios of 1.25 ‰ and a drop in δ13C ratios of 0.24 ‰ from 5-6 years of age, similar to the patterns visible in the profiles of Lim-ht-191 and Lim-ht-057 with rising δ15N ratios and dropping δ13C ratios.

When δ15N and δ13C values co-vary, a change in diet appears to be the underlying factor, which could be the result of certain cultural practices or a period of movement during which different foods were consumed. While co-varying δ13C and δ15N ratios indicate induced dietary changes, a rise in δ15N ratios combined with a decrease in δ13C ra-tios may signal nutritional stress (Neuberger et al., 2013; Beaumont et al., 2015; Beaumont and Montgomery 2016; Meier-Augenstein 2017). This pattern is visible in Lim-ht-191 between ages 9 and 15.5, where an increase of almost 2 ‰ in δ15N is combined with a drop of 0.5 ‰ in δ13C and could be linked to a nutritionally stressful phase in this in-dividual’s life, for example during prolonged illness.

However, before δ13C and δ15N ratios can be connected to potential moments of movement, more dentine profiles from individuals who are deemed local based on their strontium isotopic signature should be analysed to investigate their childhood diets and changes therein for compar-ison with the dentine profiles of these potentially four non-local individuals.

8. Who were these non-local individuals?

While the majority of the samples within our study revealed strontium isotopic values that fall within the local range, a few have non-local values. The Møgel-vang sample (Lim-ht-191) has the most radiogenic value within our dataset of 87Sr/86Sr = 0.71387 and indicates an origin outside present-day Denmark (excluding the island of Bornholm). Areas with such values can be found in, e.g., Sweden, Norway, the Danish island of Bornholm or central Europe (Nehlich et al., 2009; Frei and Frei 2013; Price and Naumann 2015; Wilhelmson and Price 2017).

At Møgelvang a ploughed over burial mound con-tained the remains of a long dolmen with NE-SW orientation from the Funnel Beaker Culture with two chambers. Although nearly all stones had been removed, marks in the ground, occasionally with remains of the stone itself, showed their original position. A battle axe from the Single Grave Cul-ture originated from the dolmen and may have belonged to a secondary interment in one of the chambers. The southern chamber was trapezoidal and roughly oriented East-West, with the wider end in the west and a passage in the east. Along the northern side of this chamber was a distur-bance, as stray objects from the Iron Age and younger periods were found here and in the holes from the removed stones. Bone material, amber beads, a small, ornamented vessel (Middle Neo-lithic I style) and flint blades were found inside the chamber. The stones used in the construction of the long dolmen seem to have been mostly gran-ite, although flat chalk stones as pavement and flat stones made of Mo-Clay were also found (pers. comm Louise Haack-Olsen). The Mo-Clay con-sisting of diatoms, clay and ash layers, is typical for the Limfjord area in Denmark (Heilmann-Claus-sen and Surlyk 2006). A recent study from Frei et al. (2019) also included strontium isotope analyses of seven individuals from the Single Grave Culture burial site of Gjerrild in eastern Jutland. One indi-vidual, a female, yielded a value that falls outside the “local” baseline range (87Sr/86Sr = 0.7127, Rise 1283) and was also interpreted as non-local. The other six individuals yielded values that fall within the “local” baseline range of present-day Denmark (Frei et al., 2019).

Samples were taken from a cranium fragment and a molar found along the western end wall of the southern chamber close to a flint blade and to the small ornamented vessel, which, however, lay in a secondary position. The cranium was dated to 2901-2586 cal BC (Appendix 2), the Middle Ne-olithic A/Single Grave Culture. While the child-hood dietary signal shows a terrestrial-based diet (δ13C = -20.9 ‰) with a low δ15N value (7.9 ‰), the adult diet shows a similar δ13C value (-20.7 ‰) but higher δ15N value (9.4 ‰) (Figure 7), signal-ling an increase of dietary protein.

The Romb tooth (Lim-ht-061) also yielded a relatively radiogenic Sr (87Sr/86Sr = 0.71203)


signal, indicating an origin outside present-day Denmark. Parts of the cranium of an adult indi-vidual of 20 ± 2 years of unknown sex were found in grave C. The burial was covered by a round mound, while other graves found in the vicinity were cremations. A bone sample from the cranium was radiocarbon dated to 675-867 cal AD (Ap-pendix 2), i.e., the Germanic/Viking Age. While the childhood diet suggests some marine protein intake (δ13C = -19.3 ‰ and δ15N = 12.8 ‰), this is reduced in the adult diet (δ13C = -20.5 ‰ and δ15N = 11.7 ‰).

Krejbjerg og Ginderup (lim-ht-057) is derived from a Passage grave, which was constructed of eight upright stones and two cap-stones, with a passage towards the east. Artefacts found in the chamber consisted of three flint axes, blades, am-ber beads and parts of several skeletons. Artefacts date to the Funnel Beaker Culture and the Single Grave Culture. The site Krejbjerg og Ginderup had two boxes in the National Museum, one with a mandible and one with the cranium, which, based on the state of preservation and discoloura-tion, appeared to belong to different individuals. Additionally, a partial maxilla is in the box with the mandible indicating a minimum of at least 2 individuals. The cranium and mandible were sampled for bone and teeth.

The non-local individual (Lim-ht-057) was radi-ocarbon dated to 3518-3123 cal BC (Appendix 2), Early/Middle Neolithic. This individual had a ter-restrial-based diet (δ13C = -20.0 ‰ and δ15N = 9.8 ‰) during their childhood, while the adult diet shows an increase in the δ13C ratio of 1 ‰, suggesting only a slight increase in marine protein intake (δ13C = -18.9 ‰ and δ15N = 10.1 ‰). The other individual (Lim-ht-058) was radiocar-bon dated to 2866-2574 cal BC (Appendix 2), the Single Grave Culture, and had a 87Sr/86Sr ra-tio right on the boundary of the Danish baseline (0.7111) proving very difficult to assess if this in-dividual is local or not. This person’s childhood diet (δ13C = -20.4 ‰ and δ15N = 9.6 ‰) was iso-topically similar to the older individual from the Passage grave, the adult diet (δ13C = -20.0 ‰ and δ15N = 9.6 ‰) does not show a shift.

Rygegård (lim-ht-072) yielded a 87Sr/86Sr ratio of 0.71111, which straddles the upper limit of the

Danish baseline range. This renders it difficult to interpret the provenance of this individual solely on this datum. Cranial fragments, including parts of the mandible and maxilla, fragments of the fe-murs, ribs and teeth were preserved, indicating a 30-50 year old male individual was buried in a stone coffin grave from the Early Roman Iron Age. A dark feature in the yellow soil was found during field ploughing. In this feature an east-west orient-ed grave was encountered with upright flat stones against the walls, one on the east and west sides, two stones on the north and south sides. Covering stones were placed on top of these upright stones. A decorated pottery piece with an ear was found inside the eastern side of the grave, while cranial fragments were encountered in the western side of the grave. Traces of bones were present on the bottom of the grave. Fragments of ornamented pottery place this grave in the Early Roman Iron Age, which is confirmed by the radiocarbon date of cranium fragments, 85-232 cal BC. Isotopi-cally, the childhood diet (δ13C = -20.1 ‰ and δ15N = 11.3 ‰) and adult diet (δ13C = -20.3 ‰ and δ15N = 10.9 ‰) are quite similar, indicating no dietary shifts.

Finally, there is an unusual type of burial that could hint at a non-local origin. The burial consisted of a flat inhumation grave with a stone frame con-tained skeletal remains of 3 individuals from the Early Roman Iron Age. Skeleton 1 belonged to an adult male individual and was positioned on the bottom of the grave with 2 clay pots and covered by a stone layer. Skeleton 2 was an adult individu-al with severe osteoarthritis found above the stone layer. Skeleton 3 belonged to an adult individual and was found during physical anthropological examination. Romdrup (Lim-ht-068) belonged to the adult male individual found under the stone layer. While this individual’s 87Sr/86Sr ratio falls within the Danish baseline range, its low Sr concentration could suggest a non-local individ-ual. A similar ‘outlier’ with low 87Sr/86Sr ratio and low strontium concentration has been pointed out by Montgomery (2010). His childhood and adult diet are very similar (childhood diet δ13C = -20.4 ‰ and δ15N = 12.1 ‰ adult diet δ13C = -20.4 ‰ and δ15N = 11.8 ‰), indicating no large dietary changes.


Three, potentially four, out of 27 individuals in this dataset have strontium isotope values that fall outside the local baseline range. Two of these individuals are from the Neolithic, one from the Early Roman Iron Age and one from the Ger-manic/Viking Age. While some degree of mobil-ity was to be expected in the Germanic/Viking Age individuals based on the results of previous studies (Price et al., 2011; 2012; 2015; Frei et al., 2014), the non-local individuals from the Neo-lithic and Early Roman Iron Age provide addi-tional insights into the degree of human mobility during those periods. Comparing the results from the present study to that of Frei et al. (2019), an interesting observation can be made. The two Neolithic individuals (Møgelvang sample Lim-ht-191 and Krejbjerg og Ginderup lim-ht-057) with non-local Sr signatures from this study were excavated in the vicinity of the individuals with non-local Sr signatures from Frei et al. (2019). Møgelvang is not far from Jestrup in Thy, while Krejbjerg og Ginderup is close to Øster Herup in Skive. While this may just be a simple coin-cidence, future strontium isotope research may shed light on potential mobility patterns in the Limfjord area and its surroundings.

9. Conclusion

Our study is the first to investigate mobility and diet of several individuals covering diachronic prehistoric periods in the Limfjord area, a key archaeological region in Denmark due to its geo-graphical location easily accessible by waterways. Of the 27 individuals analysed in this dataset, the large majority yielded Sr isotope values that point to local origin. However, three, potentially four, individuals yielded strontium isotope ratios sug-gesting a geographic origin outside present-day Denmark (the island of Bornholm excluded). This study also provided strontium isotope con-centration data of the Danish samples, which have not been published before and add useful in-formation about the potential Danish strontium sources and their characteristics.

Dietary changes were investigated through sta-ble isotope analysis of paired dentine and bone samples, as well as incremental dentine sections,

which can shed light on the childhood diet and changes therein, although nutritional stress may also leave its markers in the stable isotope ratios. As travelling in the past may have been strenuous, longer periods of nutritional stress may be appar-ent in the δ13C and δ15N profiles. However, be-fore this can be identified in the current non-local individuals, incremental dentine profiles of local individuals are needed for comparison.

This study provides new information about human mobility and diet from this key area in Denmark. However, the restricted sample size in relation to the large time scale covered by the samples prevent us, at this point, to draw broad-er conclusions. Nevertheless, the present study hopes to shed light on potential issues related to mobility.

Acknowledgements

The authors would like to thank Michelle Thompson for the stable isotope analysis, Dr Ca-triona McKenzie for aiding with the tooth iden-tification, Professor Robert Frei for access to the laboratory facilities and measurements on the TIMS at the Institute of Geosciences and Natu-ral Resource Management, University of Copen-hagen, and Michael Murphy for assistance with sample preparation and Sr isotope analyses at UCD. Laboratory facilities at UCD are support-ed in part by Science Foundation Ireland grant no. 13/RC/2092. The National Museum and Zo-ological Museum in Copenhagen, as well as the regional Museums around the Limfjord (Ålborg, Års, Skive, Mors, Thy, Holstebro and Viborg) are thanked for allowing sampling of the archaeolog-ical material. Anne-Louise Haack Olsen and Bja-rne Henning Nielsen are thanked for their com-ments on the manuscript.

This research was funded by the Leverhulme Trust (RPG-2012-817). Karin M. Frei is also thankful for the support of the Carlsberg Foundation through the “Semper Ardens” research grant CF18-0005.The authors declare no conflicts of interest.


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Appendix 1. Stable isotope results

Table 1. δ13C and δ15N ratios from human incremental dentine samples and corresponding bone samples.Sample number

Sample name and Increment number

δ15N (‰)

δ13C (‰)

C:N Dentine yield (%)

Bone number δ15N (‰)

δ13C (‰)

Period

Lim-ht-054 Øslev 5 9.0 -21.5 4.0 62.7 Lim-hb-095 8.7 -20.4 SGKLim-ht-055 Torsholm A 12 10.1 -16.7 3.6 59.0 Lim-hb-049 8.9 -18.0 ENLim-ht-056 Torsholm B 10 10.2 -18.5 3.4 46.6 Lim-hb-048 8.8 -18.6 ENLim-ht-057 Krejbjerg og Ginderup 11 9.8 -20.0 3.2 29.2 Lim-hb-044 10.1 -18.9 EN/MNLim-ht-058 Krejbjerg og Ginderup 7 9.6 -20.4 3.2 36.3 Lim-hb-045 9.6 -20.0 SGKLim-ht-059 Bjørnsholm Vitskøl 17 8.8 -19.4 3.3 69.7 Lim-hb-004 8.6 -20.2 NeoLim-ht-062 Færkærhede 12 8.5 -19.1 3.2 22.2 Lim-hb-005 8.3 -19.5 LNLim-ht-191 Møgelvang 12 7.9 -20.9 3.2 46.9 Lim-hb-148 9.4 -20.7 SGKLim-ht-192 Højvang Mark 13 8.1 -20.2 3.2 83.2 Lim-hb-153 8.9 -20.5 SGKLim-ht-060 Nørtørp 15 9.3 -20.1 3.3 40.8 Lim-hb-024 9.2 -20.1 EBALim-ht-063 Følhøj 19 8.7 -19.7 3.3 42.3 Lim-hb-042 8.9 -20.2 EBALim-ht-064 Rærgård 10 9.9 -19.8 3.2 26.9 x EBA

Lim-ht-189 Nørhå 11 11.8 -19.8 3.3 29.4 Lim-hb-138 11.6 -20.0 BALim-ht-065 NørreTranders 12 11.4 -19.4 3.3 30.8 Lim-hb-107 11.4 -20.1 ERIALim-ht-066 Nørre Tranders 13 11.9 -19.8 3.2 37.4 Lim-hb-112 11.5 -19.9 ERIALim-ht-068 Romdrup 7 12.1 -20.4 3.3 28.8 Lim-hb-113 11.8 -20.4 ERIALim-ht-070 Korsø 13 10.8 -19.6 3.3 33.8 Lim-hb-019 10.1 -20.2 ERIALim-ht-072 Rygegård 12 11.3 -20.1 3.3 25.0 Lim-hb-105 10.9 -20.3 ERIALim-ht-071 Vandet skole 11 11.6 -19.9 3.3 37.1 Lim-hb-036 11.0 -20.2 LRIALim-ht-073 Klim 10 11.9 -21.6 3.7 17.5 Lim-hb-017 10.6 -20.5 LRIALim-ht-074 Gammel Hasseris 18 12.5 -20.5 3.4 30.2 Lim-hb-006 11.0 -20.2 LRIALim-ht-061 Romb 12 12.8 -19.3 3.2 43.9 Lim-hb-031 11.7 -20.5 GER/VKLim-ht-079 Aggersborg kirke 12 12.9 -19.3 3.4 23.3 Lim-hb-001 12.4 -18.8 VKLim-ht-080 Brårup 10 11.6 -19.7 3.2 38.9 Lim-hb-022 10.7 -20.3 VKLim-ht-081* Sebbersund 11 11.8 -19.0 3.2 35.1 Lim-hb-087 10.8 -20.0 VKLim-ht-193 Næsby Østergård x Lim-hb-182 failed LN

Lim-ht-194 Næsby x Lim-hb-187 failed VK

* The tooth sample Lim-ht-081 (Sebbersund) produced a 87Sr/86Sr ratio of 0.71024 (Price et al., 2012).


Table 2. Incremental dentine stable isotope analy-sis of the 4 non-local individuals.

Sample δ15N( ‰) δ13C (‰) C:N

Møgel1 9.7 -21.9 3.2

Møgel2 9.3 -21.7 3.2

Møgel3 9.0 -21.5 3.2

Møgel4 8.5 -21.4 3.2

Møgel5 8.2 -21.4 3.2

Møgel6 7.7 -21.2 3.2

Møgel7 7.5 -21.0 3.2

Møgel8 7.1 -20.9 3.2

Møgel9 6.9 -20.7 3.2

Møgel10 7.1 -20.7 3.2

Møgel11 7.5 -20.8 3.2

Møgel13 8.1 -20.9 3.2

Møgel15 8.3 -21.0 3.2

Møgel16 8.3 -21.1 3.2

Møgel17 8.2 -21.0 3.2

Møgel18 8.8 -21.2 3.2

Krej1 9.9 -20.7 3.2

Krej2 9.3 -20.6 3.2

Krej3 9.5 -20.4 3.2

Krej4 9.5 -20.4 3.2

Krej5 9.2 -20.5 3.2

Krej6 9.0 -20.5 3.2

Krej7 9.1 -20.3 3.2

Krej8 9.2 -20.2 3.2

Krej9 9.4 -20.0 3.2

Krej10 9.5 -19.9 3.2

Krej12 10.0 -20.2 3.2

Krej13 10.3 -20.2 3.2

Krej14 10.5 -20.2 3.2

Krej15 10.4 -19.9 3.2

Krej16 10.5 -19.6 3.3

Romb1 11.9 -19.8 3.3

Romb2 11.7 -19.8 3.3

Romb3 11.2 -19.8 3.2

Romb4 10.9 -19.7 3.3

Romb5 10.8 -19.7 3.3

Romb6 10.8 -19.8 3.3

Romb7 11.4 -19.7 3.3

Romb8 11.8 -19.7 3.3

Romb9 12.1 -19.7 3.2

Romb10 12.4 -19.6 3.3

Romb11 12.5 -19.4 3.3

Romb13 12.9 -19.2 3.2

Romb14 13.2 -19.2 3.3

Romb15 13.1 -19.7 3.3

Ryg1 9.6 -20.6 3.3

Ryg2 10.2 -20.5 3.3

Ryg3 10.4 -20.7 3.4

Ryg4 10.3 -20.6 3.4

Ryg5 10.3 -20.4 3.3

Ryg6 10.3 -20.2 3.3

Ryg7 10.1 -20.1 3.3

Ryg8 10.3 -20.0 3.3

Ryg9 10.5 -20.1 3.3

Ryg10 10.9 -20.2 3.3

Ryg11 11.0 -20.1 3.3

Ryg13 11.3 -20.2 3.3

Ryg14 11.4 -20.3 3.4

Ryg16 11.5 -20.3 3.3


Appendix 2. Radiocarbon dates.

Table 3. Conventional and calibrated 14C ages of the human and faunal bone collagen samples used in this study.Tooth sample number

Location Bone sample number

Lab no 14C age ± 1σ BP

14C age cal BC/AD (2σ)

Archaeological period

Remarks

Lim-ht-055 Torsholm Lim-hb-049

UBA-31955

5038 ± 40 3799-3535 cal BC

Neolithic This study

Lim-ht-056 Torsholm Lim-hb-048

UBA-31302

5065 ± 34 3920-3645 cal BC


Lim-ht-057 Krejbjerg og Ginderup

Lim-hb-044

UBA-31298

4697 ± 34 3518-3123 cal BC

Early/Middle Neolithic

This study

Lim-ht-058 Krejbjerg og Ginderup

Lim-hb-045

UBA-31299

4142 ± 33 2866-2574 cal BC


Lim-ht-059 Bjørnsholm (Vitskøl)

Lim-hb-004

UBA-31296

4303 ± 43 3022-2760 cal BC

Middle Neolithic/SGK

This study

Lim-ht-060 Nørtorp Lim-hb-024

UBA-31301

3150 ± 30 1491-1296 cal BC

Early Bronze Age This study

Lim-ht-061 Romb Lim-hb-031

UBA-31300

1259 ± 29 cal AD 675-867

Germanic/Viking Age

This study

Lim-ht-062 Færkerhede Lim-hb-005

UBA-31297

3536 ± 54 1944-1662 cal BC

Late Neolithic This study

Lim-ht-072 Rygegård Lim-hb-105

UBA-31303

1869 ± 28 85-232 cal BC

Early Roman Iron Age

This study

Lim-ht-079 Aggersborg Kirke

Lim-hb-001

K-2765 Viking Age cal AD 1030. Submitted by J. Heinemeier.

Lim-ht-189 Nørhå Lim-hb-138

UBA-31280

2902 ± 55 1212-909 cal BC

Early Bronze Age This study

Lim-ht-190 Lodbjerg klit Lim-hb-146

UBA-31285

4656 ± 49 3628-3139 cal BC

Early/Middle Neolithic

This study

Lim-ht-191 Møgelvang Lim-hb-148

UBA-31286

4180 ± 59 2901-2586 cal BC


Lim-ht-192 Højvang Mark

Lim-hb-153

UBA-31289

4001 ± 58 2838-2301 cal BC

Single Neolithic This study

Lim-ht-193 Næsby Østergård

Lim-hb-182

AAR-10059

3865 ± 60 3772 ± 60 Late Neolithic Submitted by B. H. Nielsen.

Lim-ht-194 Næsby Lim-hb-187

Viking Age

Hov, flint-mine

Early Neolithic Other material from Hov dated: Poz-7671, Poz-7675. Submitted by K.A. Soerensen

Krabbesh-olm II

Early Neolithic Other material from Krab-besholm II dated: Poz-12163, Poz-12127, Poz-26157, Lus-6138, Lus-6654, Oxa-27066 Submitted by I.B. Enghoff, K.A. Soerensen, L. Sorensen.

Smedegård Iron Age Chicken from Smedegård dated (AAR-3784) 2085 ± 45. Submitted by T. Andreasen.

Circa 2.5-3 mg of collagen was loaded with 0.09 g of copper oxide and a silver strip for contaminant removal in a small quartz tube for combustion to CO2. Combusted samples were graphitised using a hydrogen reduction method with iron as catalyst. Pressed targets were analysed together with oxalic acid standards and background samples in the NEC compact model 0.5MV AMS at the 14CHRONO Cen-tre in Belfast. Radiocarbon ages were calculated from F14C (Reimer et al., 2004), which is corrected for


background and isotopic fractionation using 13C/12C measured by AMS that accounts for both natural and machine isotopic fractionation. An error multiplier of 1.3 was applied to the F14C measurements to account for variability in sample processing. 14C dates were calibrated using Calib 7.0.2 with the mixed marine and Northern Hemisphere terrestrial curves (Reimer et al., 2013) for humans. Based on 13 known age mollusc measurements (Olsson 1980; Heier-Nielsen et al., 1995) from the Limfjord area tak-en from the marine reservoir database (http://calib.org/marine/), the ΔR and uncertainty were calculated (ΔR = 239 ± 164 yrs). The percentage of marine carbon was calculated using a linear regression between a fully marine and terrestrial endmember based on δ13C ratios from marine and terrestrial animals.

References

Heier-Nielsen, S., Heinemeier, J., Nielsen, H.L., Rud, N., 1995. Recent reservoir ages for Danish fjords and marine waters. Radiocarbon, 37(3), 875-882. https://doi.org/10.1017/s0033822200014958

Olsson, I.U., 1980. Content of 14C in marine mammals from Northern Europe. Radiocarbon, 22(3), 662-675. https://doi.org/10.1017/s0033822200010031

Reimer, P.J., Baillie, M.G.L., Bard, E., Bayliss, A., Beck, J.W., Bertrand, C., Blackwell, P.G., Buck, C.E., Burr, G., Cutler, K.B., Damon, P.E., Edwards, R.L., Fairbanks, R.G., Friedrich, M., Guilderson, T.P., Hughen, K.A., Kromer, B., McCormac, F.G., Manning, S., Bronk Ramsey, C., Reimer, R.W., Remmele, S., Southon, J.R., Stuiver, M., Talamo, S., Taylor, F.W., Van der Plicht, J., Weyhenmeyer, C.E., 2004. INTCAL04 Terrestrial Radiocarbon Age Calibration, 0-26 Cal KYR BP, Radiocarbon, 46, 1029-1058. https://doi.org/10.1017/S0033822200032999

Reimer, P.J., Bard, E., Bayliss, A., Warren Beck, J., Blackwell, P.G., Bronk Ramsey, C., Buck, C.E., Cheng, H., Lawrence Edwards, R., Friedrich, M., Grootes, P.M., Guilderson, T.P., Haflidason, H., Hajdas, I., Hatté, C., Heaton, T.J., Hoffmann, D.L., Hogg, A.G., Hughen, K.A., Felix Kaiser, K., Kromer, B., Manning, S.W., Niu, M., Reimer, R.W., Richards, D.A., Marian Scott, E., Southon, J.R., Staff, R.A., Turney, C.S.M., Van der Plicht, J. 2013. INTCAL13 and MARINE13 Radiocarbon Age Calibration Curves 0-50,000 Years Cal BP. Radiocarbon, 55, 1869-1887. https://doi.org/10.2458/azu_js_rc.55.16947

mobility and diet in prehistoric denmark: strontium

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